As an excavating tool which inserts a casing pipe concurrently with ground excavation, in PTLs 1 and 2, the present inventors have proposed an excavating tool in which a ring bit is rotatable with respect to a casing pipe and is locked in a direction of an axis line of the casing pipe by using locking means such as a locking member so that the ring bit does not inadvertently fall out during excavation. This excavating tool carries out excavation work by transmitting rotating force applied to an inner bit to the ring bit and by transmitting thrust force or striking force applied to a distal end side of the inner bit in the direction of the axis line to the casing pipe and the ring bit. The thrust force or the striking force from the inner bit to the ring bit is transmitted via the casing pipe or directly.
In the excavating tool whose ring bit is locked in the direction of the axis line in the distal end of the casing pipe in this way, there is no problem when the casing pipe is left inside the bore. However, when the casing pipe is temporarily inserted into the bore and the used casing pipe is lifted up from the bore so as to be collected on the ground, such as when the casing pipe is replaced with a building member or is used as a temporary pile, there is a possibility that efficient collection may be difficult. This is because the ring bit locked in the distal end of the casing pipe causes an increase in resistance between an inner peripheral surface of the bore and the ring bit due to its outer diameter larger than that of the casing pipe, thereby excessive lifting force is required.
Therefore, in PTL 3, the present inventors have further proposed the excavating tool in which the above-described locking means includes a pulling-out mechanism for pulling out the ring bit from the casing pipe to the distal end side in the direction of the axis line, and which causes the pulling-out mechanism to pull out the ring bit from the casing pipe to the distal end side in the direction of the axis line after the bore into which the casing pipe is inserted is formed to reach a predetermined depth. According to this excavating tool, the ring bit is removed by being pulled out from the distal end of the casing pipe. In this manner, without causing the increased resistance between the inner peripheral surface of the bore and the ring bit, it is possible to lift up and collect only the casing pipe from the bore.